In recent years, assembly automation has progressed for products having a small size and complex structure, such as cameras, which raises a demand for a small-size industrial robot for performing high-speed and precise assembly with fine control of force. In a conventional case, in order to assemble a gripped part precisely and reliably, a force sensor for detecting a force based on a change in output caused by displacement of a member is provided between a robotic arm and an end effector, to thereby control the arm and the end effector while detecting the force at the time of assembly by using the force sensor (see PTL 1).
FIG. 7 illustrates the related art. The force control robot according to the related art includes a robotic arm 502, a force sensor 510, an end effector 501, and other components. The force control robot uses the end effector 501 to grip a part O, and assembles the gripped part O to a workpiece Q. The robotic arm 502 is driven by a driver 523, and a controller 524 is provided so as to input an operation signal and a position control signal for the robotic arm 502 to the driver 523.
The force sensor 510 includes an arm-side plate 511 fixed to the tip end of the robotic arm 502, an end-effector-side plate 512 fixed to the end effector 501, and an elastic member 513 for coupling and supporting both the plates 511 and 512. The force sensor 510 also includes a displacement detection mechanism between the plates 511 and 512. The displacement detection mechanism includes, on the arm-side plate 511, a beam 514 having a crossed tip end portion and extending toward the end-effector-side plate 512.
In the force control robot of the above-mentioned related art, the force sensor 510 is serially arranged between the robotic arm 502 and the end effector 501. Accordingly, the rotation center of the end effector 501 relative to the robotic arm 502, which exists inside the force sensor 510, is positioned apart from the center of gravity of the end effector 501. Therefore, due to the inertial force at the time of driving the robotic arm 502, the moment force generated by the positional difference between the displacement fulcrum of the elastic member 513 and the center of gravity of the end effector 501 is applied to the force sensor 510. As a result, the period of time to be required until the sensor portion is stabilized is long.
In order to reduce the stabilization period, it is necessary to increase the rigidity of the elastic member 513 of the force sensor 510. As a result, the sensor becomes less sensitive to the external force, leading to a decrease in detection sensitivity of the force sensor 510. In other words, precise force detection is difficult when the rigidity of the elastic member is increased. Thus, with the above-mentioned structure of the related art, as the end effector is downsized, it becomes difficult to attain both increasing the detection sensitivity of the sensor and ensuring a rigidity for supporting high-speed operation.
The present invention provides such a force control robot that an end effector can be downsized easily and high-speed operation can be supported with no decrease in detection sensitivity of a force sensor.